ERR(3) NetBSD Library Functions Manual ERR(3)
NAMEerr, verr, errx, verrx, warn, vwarn, warnx, vwarnx -- formatted error
messages
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS#include <err.h>voiderr(int status, const char *fmt, ...);
voidverr(int status, const char *fmt, va_list args);
voiderrx(int status, const char *fmt, ...);
voidverrx(int status, const char *fmt, va_list args);
voidwarn(const char *fmt, ...);
voidvwarn(const char *fmt, va_list args);
voidwarnx(const char *fmt, ...);
voidvwarnx(const char *fmt, va_list args);
DESCRIPTION
The err() and warn() family of functions display a formatted error mes-
sage on the standard error output. In all cases, the last component of
the program name, a colon character, and a space are output. If the fmt
argument is not NULL, the formatted error message is output. In the case
of the err(), verr(), warn(), and vwarn() functions, the error message
string affiliated with the current value of the global variable errno is
output next, preceded by a colon character and a space if fmt is not
NULL. In all cases, the output is followed by a newline character. The
errx(), verrx(), warnx(), and vwarnx() functions will not output this
error message string.
The err(), verr(), errx(), and verrx() functions do not return, but
instead cause the program to terminate with the status value given by the
argument status. It is often appropriate to use the value EXIT_FAILURE,
defined in <stdlib.h>, as the status argument given to these functions.
EXAMPLES
Display the current errno information string and terminate with status
indicating failure:
if ((p = malloc(size)) == NULL)
err(EXIT_FAILURE, NULL);
if ((fd = open(file_name, O_RDONLY, 0)) == -1)
err(EXIT_FAILURE, "%s", file_name);
Display an error message and terminate with status indicating failure:
if (tm.tm_hour < START_TIME)
errx(EXIT_FAILURE, "too early, wait until %s",
start_time_string);
Warn of an error:
if ((fd = open(raw_device, O_RDONLY, 0)) == -1)
warnx("%s: %s: trying the block device",
raw_device, strerror(errno));
if ((fd = open(block_device, O_RDONLY, 0)) == -1)
warn("%s", block_device);
SEE ALSOexit(3), getprogname(3), strerror(3)HISTORY
The err() and warn() functions first appeared in 4.4BSD.
CAVEATS
It is important never to pass a string with user-supplied data as a for-
mat without using `%s'. An attacker can put format specifiers in the
string to mangle your stack, leading to a possible security hole. This
holds true even if you have built the string ``by hand'' using a function
like snprintf(), as the resulting string may still contain user-supplied
conversion specifiers for later interpolation by the err() and warn()
functions.
Always be sure to use the proper secure idiom:
err(1, "%s", string);
NetBSD 6.0 March 21, 2001 NetBSD 6.0

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